The present invention relates to a brightness control device for use in lamps of the type in which light is emitted by means of a fiber optical conductor, i.e., the so-called fiber optical lamps.
It is known in the art that the brightness of the light emitted by fiber optical lamps may be controlled by inserting a variable resistance or a regulating transformer into the circuit of the lamp, or by utilizing phase-shifting controls for this purpose. With each of these arrangements, the operating voltage of the lamp and thus the color temperature of the light emitted is altered, although the emission characteristics of the fiber optical conductor or conductors, respectively, are preserved, i.e., the angle of radiation and the magnitude of the illuminated area are maintained constant.
It is also known to effect the regulation of brightness by means of a built-in iris diaphragm. With this arrangement, the color temperature of the lamp remains constant, but the angle of radiation of the optical fiber conductor is changed.